Devices for cutting off successive lengths of a continuously moving, elongated workpiece such as tubing emanating from a mill, are well known in the art. Typically, the tube cut-off device comprises a die set mounted on a carriage for selective motion along the length of the tubing. The die set and carriage are mounted on a flying type ram operated in synchronism with the movement of the tubing. In a typical prior art apparatus such as that disclosed in Patent No. 3,938,415, the disclosure of which is hereby incorporated by reference, a dual step cutting sequence is employed. A first stage in the cutting is accomplished by a prepiercing mechanism which includes a piercing blade which is reciprocated across the upper periphery of the tubing after the tubing is clamped within die set clamping jaws and just prior to the descent of the main cut-off blade. Prepiercing the tubing eliminates dimpling of the tubing, often resultant from prior art single stroke "guillotine-type" cut-off devices.
In the above-described double cut tube cut-off apparatus the tubing is first clamped by die jaws operated by means of the ram mechanism which drives a vertically extending cam between cam surfaces. This causes reciprocal motion of the die jaw mounts toward one another effecting the clamping of the tube therebetween as disclosed in the above identified patent. Since the tubing is clamped within the die set for only a short time interval and because the piercing blade must be removed from the path of the descending cut-off blade before severing can be effected, the movement of the piercing blade is very rapid. Control of the blades at high speed presents various problems. Also in some instances, the path of travel of the severing blade may not be precisely aligned with that of the piercing blade, either due to wear over an extended period of use or as a result of errors in original manufacturing tolerances. In the case of minor misalignment in the paths of travel of the piercing and severing blades, the severing blade may initially engage the exterior side wall of the tubing along the edge of the pierce rather than penetrating the pierce itself resulting in a dimpling of the tubing. Additionally, misalignment of the severing blade relative to the piercing blade increases wear of the severing blade and produces additional drag on the severing blade, since the blade may frictionally engage the blade supporting surfaces of the clamping members.
A further problem is created by the high velocity of the piercing blade inasmuch as this creates considerable heating of the piercing blade, leading to relatively rapid wear thereof.
U.S. Pat. No. 4,015,496 of Hill discloses a tube cut-off apparatus in which a single blade of the apparatus effects the notching and severing of the tubing in two distinct strokes. The apparatus includes means for moving the blade in a first direction to notch the tube and in a second direction to sever the notched tube at a point commencing with the previously formed notch.
Hill employs a cut-off blade having a generally horizontal notching tip portion and severing portions diverging therefrom. Hill teaches that the blade first travels horizontally across a chord of the tube to notch it, then for the second stroke, the blade returns to the initial precut position and is driven downward at an angle of 90.degree. to the first direction of travel to complete the cutting of the tube. With this type of dual stroke operational sequence, problems with blade misalignment after the notch has been made as well as excessive blade wear due to the rapid velocities involved tend to create blade failures as well as high rates of blade wear, similar to the dual blade apparatus.
It can therefore be seen that there is yet a need for a single blade tubing cut-off apparatus which effects the piercing and severing of continuously moving tubing in a single stroke without dimpling of the tubing. The present invention addresses these problems by providing a single blade, single stroke tube cut-off apparatus wherein the blade of the apparatus is first driven by means of a cam follower against a cam surface in a vertical direction to pierce the tube and which subsequently moves at an angle to this first direction without return to its initial position to complete the severing of the tube in one stroke. In this manner, dimpling of the tubing during the severing thereof is eliminated. The present invention also provides novel means for clamping the workpiece in die jaws utilizing spring biased means to pivot the die jaws to the clamped position.
These and other advantages of the present invention will be apparent from the discussion, drawings, description and claims which follow.